The present invention relates to a melt pump used in a kneading granulating apparatus for boosting melted resin between a kneading machine and a pelletizer. 2. Description of the Prior Art
The melt pump is used to boost the pressure of melted resin at 200.degree. to 300.degree. C. delivered from a kneading machine up to 200 to 300 kg/cm.sup.2 and to supply it to a pelletizer. Consequently, it needs to meet the high temperature/high pressure specifications, and particularly, to have the seal structure of special design.
In FIG. 5, the gear rotor 6 is supported on a pair of bearing bodies 30. Lubrication of these bearing bodies 30 is achieved by melted resin forcibly supplied by the discharge pressure. Then, clearances are positively formed between the pump housing 3 and the gear rotor 6. Melted resin leaking through these clearances 7 is made to flow into the intake port of the pump housing 3 to be recovered.
In the technique of the prior art, resin flowing through the clearances 7 sometimes makes exothermic action by receiving shearing action, resulting in deterioration of its quality. Therefore, a cooling hole 9 is formed inside the gear rotor 6, and a pipe 10 is inserted in the cooling hole 9, thus cooling the gear rotor 6 side with cooling liquid.
As described above, in the prior art, deterioration of recovered resin due to its exothermic action can be prevented. However, the prior art is disadvantageous in that adverse affects influenced by cooling on the gear rotor 6 often occur. The melt pump must meet the high temperature/high pressure specifications, and employs the gear rotor composed of high tension steel such as SNCM material. The central portion of the high tension steel is sometimes cooled with industrial water containing impurities. This induces a fear of yielding heat shock, stress corrosion, corrosive fatigue, etc. on the gear rotor 6, resulting in cracks on the internal periphery of a cooling hole.